Lingjun Chou

Surface WO4 tetrahedron: the essence of the oxidative coupling of methane over M-W-Mn/SiO2 catalysts

Abstract A series of MWMn/SiO2 catalysts (M = Li, Na, K, Ba, Ca, Fe, Co, Ni, and Al) have been prepared and their catalytic performance for the oxidative coupling of methane (OCM) was evaluated in a continuous-flow microreactor. The structural properties of the catalysts have been studied using X-ray photoelectron spectroscopy (XPS), laser Raman spectroscopy (LRS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). In the trimetallic catalysts studied, there was evidence for WO4 tetrahedron on the surface in the Li, Na, and KWMn/SiO2 catalysts, which is mainly present in the subsurface of the BaWMn/SiO2 catalyst. It appears that the WO4 has a strong interaction with the α-cristobalite support and is stabilized in the Na and KWMn/SiO2 catalysts. However, the WO4 species appear to be less stable in Li or BaWMn/SiO2 catalysts, in which the support turns into quartz SiO2 or amorphous SiO2. The WO4 tetrahedron on the catalyst surface appears to play an essential role in achieving high CH4 conversion and high C2 hydrocarbon selectivity in the OCM reaction. Calculations suggest that the WO4 tetrahedron interacts with the CH4, giving suitable geometry and energy matching with CH4, and this may account for the high OCM activities.

Catalytic conversion of cellulose to chemicals in ionic liquid

A simple and effective route for the production of 5-hydroxymethyl furfural (HMF) and furfural from microcrystalline cellulose (MCC) has been developed. CoSO(4) in an ionic liquid, 1-(4-sulfonic acid) butyl-3-methylimidazolium hydrogen sulfate (IL-1), was found to be an efficient catalyst for the hydrolysis of cellulose at 150°C, which led to 84% conversion of MCC after 300min reaction time. In the presence of a catalytic amount of CoSO(4), the yields of HMF and furfural were up to 24% and 17%, respectively; a small amount of levulinic acid (LA) and reducing sugars (8% and 4%, respectively) were also generated. Dimers of furan compounds were detected as the main by-products through HPLC-MS, and with the help of mass spectrometric analysis, the components of gas products were methane, ethane, CO, CO(2,) and H(2). A mechanism for the CoSO(4)-IL-1 hydrolysis system was proposed and IL-1 was recycled for the first time, which exhibited favorable catalytic activity over five repeated runs. This catalytic system may be valuable to facilitate energy-efficient and cost-effective conversion of biomass into biofuels and platform chemicals.

Hydrolysis of cellulose in SO3H-functionalized ionic liquids

Influence of acidity and structure of ionic liquids on microcrystalline cellulose (MCC) hydrolysis was investigated. MnCl₂-containing ionic liquids (ILs) were efficient catalysts and achieved MCC conversion rates of 91.2% and selectivities for 5-hydroxymethyl furfural (HMF), furfural and levulinic acid (LA) of 45.7%, 26.2% and 10.5%, respectively. X-ray diffractometry indicated that catalytic hydrolysis of MCC in ionic liquids resulted in the changes to MCC crystallinity and transformation of cellulose I into cellulose II. SO₃H-functionalized ionic liquids showed higher activities than non-functionalized ILs. The simplicity of the chemical transformation of cellulose provides a new approach for the use this polymer as raw material for renewable energy and chemical industries.

Methanation of Carbon Dioxide over a Highly Dispersed Ni/La2O3 Catalyst

The methanation of carbon dioxide on a Ni/La2O3 catalyst containing 10 wt% Ni prepared by the impregnation method was studied. The space-time yield of methane was 3000 g/(kg·h) at conditions of 350 °C, GHSV of 30000 h−1, 1.5 MPa pressure, and H2/CO2 molar ratio of 4. The selectivity for methane was 100% with different CO2 conversions. Combined with X-ray diffraction and H2 temperature-programmed reduction analyses, this suggested that the reaction mechanism on Ni/La2O3 may be different from that on Ni/γ-Al2O3. The formation of lanthanum oxycarbonate (La2O2CO3) can play an important role in the activation of CO2.

Dehydration of fructose into 5-hydroxymethylfurfural in acidic ionic liquids

A simple and effective process for the dehydration of fructose into 5-hydroxymethylfurfural (HMF) using ionic liquid 1-(4-sulfonic acid) butyl-3-methylimidazolium hydrogen sulfate (IL-1) as the catalyst was developed. High fructose conversion of 100% with HMF yield of 94.6% was obtained at 120 °C for 180 min reaction time in water-4-methyl-2-pentanone (MIBK) biphase system. Generally, the increase of water content had a negative effect on the reaction, the HMF selectivity decreased as the excessive elevation of temperature and prolonging of time, which suggested the decomposition of HMF. The ionic liquid IL-1 could be recycled and exhibited constant activity for six successful runs. This paper provided a new strategy for HMF production from fructose.

Influence of SnO2-doped W-Mn/SiO2 for oxidative conversion of methane to high hydrocarbons at elevated pressure

The SnO2-doped 5% Na2WO4-2% Mn2O3/SiO2 catalyst for oxidative conversion of methane to high hydrocarbons has been studied in a micro-stainless-steel reactor at elevated pressure. At 1053 K, 1.0 t 105 hm1 GHSV and 0.6MPa, a CH4 conversion of 33.0% with C2+ selectivities of 73.1% is obtained; here the C2, C3 and C4 hydrocarbons selectivities of 36.8, 14.2 and 22.1% are observed. On addition of SnO2, conversion of methane and selectivities of C3nC4 hydrocarbons increase obviously. The observed results showthe storage-oxygen capability in Na-W-Mn/SiO2 catalyst is enhanced with adding SnO2, for Mn and Na2WO4 migrate to near-surface to result in a marked shift to higher molecular weight products. The distribution of products at the operating conditions and content of SnO2 loading has been described.

Oxidative coupling of methane over Na-Mn-W/SiO2 catalyst at higher pressure

Na-Mn-W/SiO2 catalysts were prepared and their catalytic performance for oxidative coupling of methane (OCM) was evaluated in a stainless-steel microreactor at elevated pressure. The results show that a CH4 conversion of 15.1% with a C2+ selectivity of 71.8% was obtained under 750oC, 1.0×105h-1 GHSV, CH4/O2 ratio of 8 and 1.0 MPa. Moreover, 17.3% CH4 conversion with 51.6% C2 selectivity and 23.6% C3-C4 selectivity was obtained under 750oC, 2.0×105h-1 GHSV, CH4/O2 ratio of 8 and 1.0 MPa.

Selective Conversion of Methane to C2 Hydrocarbons Using Carbon Dioxide over Mn-SrCO3 Catalysts

The combination of Mn with SrCO3 leads to effective catalysts for the selective conversion of CH4 to C2 hydrocarbons using CO2 as an oxidant; C2 selectivities approach 88 and 79.1% with a C2 yield of 4.3 and 4.5% over catalysts with an Mn/Sr ratio of 0.1 and 0.2, respectively. It is assumed that the Mn3+/Mn2+ couple formed in the reaction plays an important role in the activation of CO2 and CH4.

Characterization and performance of Cu/ZnO/Al2O3 catalysts prepared via decomposition of M(Cu, Zn)-ammonia complexes under sub-atmospheric pressure for methanol synthesis from H2 and CO2

Abstract Methanol synthesis from hydrogenation of CO2 is investigated over Cu/ZnO/Al2O3 catalysts prepared by decomposition of M(Cu, Zn)-ammonia complexes (DMAC) at various temperatures. The catalysts were characterized in detail, including X-ray diffraction, N2 adsorption-desorption, N2O chemisorption, temperature-programmed reduction and evolved gas analyses. The influences of DMAC temperature, reaction temperature and specific Cu surface area on catalytic performance are investigated. It is considered that the aurichalcite phase in the precursor plays a key role in improving the physiochemical properties and activities of the final catalysts. The catalyst from rich-aurichalcite precursor exhibits large specific Cu surface area and high space time yield of methanol (212 g/(Lcat · h); T = 513 K, p = 3 MPa, SV = 12000 h−1).

Oxidative coupling of methane over BaCl2-TiO2-SnO2 catalyst

The performance of BaCl 2 -TiO 2 -SnO 2 composite catalysts in oxidative coupling of methane reaction has been investigated. A series of BaCl 2 -TiO 2 , BaCl 2 -SnO 2 , TiO 2 -SnO 2 , and BaCl 2 -TiO 2 -SnO 2 catalysts were prepared, and characterized by BET, XRD, XPS, CO 2 -TPD and H2-TPR, respectively. The synergistic effect among BaCl 2 , SnO 2 and TiO 2 compositions enhances the catalytic performance. The best C2 selectivity and ethylene yield are obtained on the catalyst with the equal molar amount of the three compositions (BaCl 2 : TiO 2 : SnO 2 molar ratio of 1:1:1). The optimal reaction conditions are as follows: 800°C, 44 mL-min −1 for methane, 22 mL-min −1 for oxygen and a space velocity of 5000 mL-h −1 -g −1 , and the C 2 H 4 yield over the catalyst is 20.1% with the CH 4 conversion of 43.8% and C2 selectivity of 53.3%.